HOW BUTLER DID IT

For all the computer-generated wizardry that went into the stylized look of Warner Bros.' "300," opening today, it was old-fashioned discipline and drudgery that turned actor

Gerard Butler into a Spartan warrior king.

Realizing he would have to parade around bare-chested for most of the movie adaptation of Frank Miller's (extremely) graphic novel, the 37-year-old Scotsman trained six hours a day for almost eight months. If Butler was to convincingly play King Leonidas, who led the titular small band of soldiers against a million invading Persians in 480 B.C., he wanted to look the part.

"I knew to get that extreme power, and exude that authority and leadership and that potential violence and brutality, that I wanted to earn that," said Butler, best known for playing the title role in 2004's "The Phantom of the Opera."

"I wanted to really know that I had it and not feel like one of those public-school boy actors standing up there, pretending to be tough and pretending to be big, and having the men pretending to respect him."

So Butler started his intense regimen four months before a one-month boot camp designed to turn Hollywood actors into Spartans, and continued throughout the 60-day shoot. There were two-hour sword-fighting sessions with the film's stunt men; squat thrusts with weights and chains; having to watch the crew eat desserts off the catering spread while actors were on forced diets.

Worst of all was the dreaded bear crawl, in which the actors had to race around on hands and feet after their legs were quivering from squats. Butler tore his hip flexor muscle doing that drill.

"Pretty much anything Mark Twight [the production's trainer] offered up was so difficult in the kind of way where you wish you had never been born - and even more than that, wished he had never been born," said Butler.

"You don't look at a bunch of Spartans and go, 'I wonder which guy is going to pop out and be the king,'" said Zack Snyder, the film's director. "In one shot you want to go, 'Okay, that's him,' and that was how I felt about Gerry."